Selective telegraph system



Aug. 24, 1943.

c. R. WALKER SELECTIVE TELEGRAPH SYSTEM Filed July 25, 1942 TTY INVENTOR C. H, Wad/sel BY 6 ATTORNEY Patented Aug. 24, 1943 SELECTIVE TELEGRAPH SYSTEM Charles Robert Walker, Jersey City, N. J.,' as Signor to American Telephone andTclegraph Company, a corporation of New York Application July 23, 1942, Serial No. 52,007

' (Gina-2) 6 Claims.

This invention relates to telegraph and teletypewriter systems. This invention also relates to repeaters for telegraph and. teletypewriter systems. Moreover, this invention relates to telegraph and teletypewriter systems arranged for the selective transmission of signals.

In telegraph systems in which repeaters are employed to interconnect two main stations it'is sometimes necessary to connect a telegraphloop of the usual type at an intermediate point in the circuit between the loop terminals of the repeaters at that point so that all of the signals transmitted between the two main stations through the repeaters will also be received in the loopcircuit and all signals emanating from the loop circuit will be transmitted through the repeaters to the two main stations. It is sometimes necessary to receive all signals emanating from the loop circuit to the exclusion of all signals transmitted between the two main stations through the repeaters. A simple arrangement to permit the reception of signals emanating from the loop circuit is the subject of the present invention,.

and the arrangement is intended to be non-responsive to all signals transmitted in either direction between the two main stations.

According to the present invention the loop circuit connected between two telegraph repeaters is bridged by a circuit including a vacuum tube, the grid and cathode of which'are connected across the telegraph loop circuit in serieswith a source of biasing voltage of suitable magnitude. The plate circuit of the vacuum tube is connected through the operating winding of a, relay of,

for example, the neutral type. The arrangement is set up so that as signals are transmitted through the repeaters from either of the two main stations, these signals will be received by the telegraph loop circuit, butthe voltage across the grid and cathode of the tube will be insufficient to permit a flow of currentdn the plate circuit of the vacuum tube. However, when'si'gnals are emanating from the loop circuit they will not only be transmitted to the two main stations above referred to, but thosesignals will produce voltages across the grid and cathode of the vacuum tube sufficient to overcome the biasing voltage, thus permitting current to flowin the plate circuit of the vacuum tube. These signals will then be reproduced, in the plate circuit of the vacuum tube, thus causing'the neutral relay to follow the telegraph signals. These signals maybe repeated over any form of circuit. The

circuit controlled by the polar relayis thus sele'c-- tively responsive only to the signals arriving from the loop circuit.

This invention will be better understood from the more detailed description hereinafter following whenrread in connection with the accompanying'drawing showing one embodiment of the invention merel for the purpose of illustration.

Referring to the drawing, central ofiice telegraph repeaters are shown which include two equal sending relays SR1 and SR2 and two equal receiving relays BB1 and RR2. The sending relays SR1 and SR2 include two windings, the upper or main windings of which are connected to a telegraph loop L1-L2 through resistors Z1 and Z2, respectively; The lower windings of relays SR1 and SR2 are connected to. ground through the usual balancing networks BN1 and BN2, respectively, which are of well-known type. The apex of the windings of the relays SR1 and SR2 are connected tothe armatures of relays RR1 and RRz, respectively. The armatures of relays SR1 and SR2 are connected to the apeXes of relays BB1 and BB2 respectively. The; lower winding of relays RRi and RRZ are connected through the balancing networks BN2 and EN; to ground in the usual manner. The armature of relay RRrmay be caused to move between its marking and spacing contacts Mend S to connect oppositely poled batteries B1 and B2 to the apex of the windings of relay SR1. Similarly the armature of relay RPtzfma be caused to move betweenits marking and spacing contacts M and S to connect oppositelypoled batteries B3 and B4 to the apex of the windings of relay SR2.

The upper or main winding of relay BB1 is connected in series with the teletypewriter TTYi and the battery B5 and the upper or main wind ing of relay RRz'is connected in series with the teletypewriter TTYz and the battery Be. The telegraph loop circuit L1L2 may include a teletypewriter TTYo which may be the same as teletypewriters TTY1 and TTYz, including, for example, a magnet MG for recording all signals traversing the loop circuit L1--L2 in a wellknown manner and a contact apparatus TC for transmitting signals in a well-known manner romthe teletypewriter TTY through the two branches oi the telegraph repeater to the main stations having the teletypewriters TTY1 and TTYz. V

. The circuit so far described is of well-known type. The present invention resides in connectingacross-the points P1P2 a vacuum tube systern for receiving signals coming from the loop and marking' contact. M: or reLay -B an-d'greund. The armature of biase'dby a spring to-its mark g-aco-ntact the negative terminal thereof is connectecltothe grid electrode. The plate circuit of thetubefl includes the usual plate battery B12 and the winding of a neutral relay R0 arranged'inseriesrelaticnship, the armature of the relay R0 being'connected to a telegraph circuit L3 which will receive signals thatactuate the winding cfrelay'R In the idle condition of the the arma- -"tures-of relays R31 and RRa are z-Jonnected to the r marking contacts M so that-a substantial ent will flow through the or'mai'n 'wind-ing-s of relays SB1-andSBa 'this circuit including battery 131, the marking oontac't an d armature of relay RR1, the upper winding ofrelay SR1, resistor -21, loop conductor L11, the tele- T'PYo, l loop conducter L2, =resistor Z2, upperwinrimgoi relay hearmature battery B3 ayiRmmaybe shown.

Marking-and spacing signals :coming'i-romteietypw -ri ter TT'Y1 will-cause current .to flow cal- *tenntttely through the upper winding :of relay RRL 'tween its markings-and spacing oonta cts maands "in res-ponse to theseflsigrrais, it IWillconnect top- As the. armature relay BB1 .znoves bepos ite'ly spo led batteries to the. circuit-10f .the upor rnainwindings of relays SRL andL SRz and :to me teletypetvriter TIE-Yo raflwve described. In-

asmuch :as-these :signalsare neceive'dlbythe mag- .ne't MG of theiteletypewliiter:TI'Yn,.:tlrey iwillbe printed by the teletypewii'ter iTTYt: in the usual I -As these currentstraverse the upper "wan-ding of vrel'ayssRz, ithey scaiuse'th-e armature of relay SR2 to move :;between its Jmarlting and signals to the rteletypewriter IETYzz. Simii-ar'ly mc-arking and spacing-signals 'C'O'TiliflEIfilGiflliliEll'E- -typewr iter iTTYz rsvi'll .loe ."tramsmittediiizcatirei' teletypewriter TWO 1 to .the ELF-LL2- g= contacts 1M and-5S so :as to repeat'the and to te etmewriter :It will-lbs observed ;that :the circuit interconnectingthe :uppertor mainWvindingsoirel-ays SR1 :emd :SRaabove describedin'clurles twoimpedances 1Z1 and=Zz;each of whichmay be, frorrexamnle-pf 6 ohms, the I'OE'QIE iTEEii ;.L1-+'L2-.w-hi'ch xample, ofiiibl) ohms. PT eseiare pedances inclufiedinithis: circuit, :nces be ng of relatively insignificant magnitudes. It will also be observed-that the voltage hetween points P1 and'Pe 'of this-circuit will vary from a "zero tude vvhich is-equal to the s two of the batteries Brto EBi, as willnowbe explained.

ntude toa magniof the voltages of a The voltage across points P1 and P2 will be of zero magnitude when-a spacing signal i's'being transmitted-imam: one or. the tcletypewriters-such as TTY1 through the-repeaters. to the teletypewriter"I'TYQ, in=which-case the batteries Bz and .to approximately 65 volts. ,pointPz will be positive with respect to the pothrough the repeaters.

respect to .point ;P1. overcome the biasing potential of battery B11 and will therefore-render the grid electrode ofv tube V positive with respect toits cathode. Consequent- ..ly va substantial current will flow through the plate circuit of tube V, and, therefore, operate the vrelay Ro-SO as .to close its spacing contact-S. This voltage between points P1 and P2.

will then bereleased so that the armature will B3Whlch are of equal potential and of the same polarity-are connected to the points P1 and P2 and to the circuit of the main windings of relays SR1 and SR2. The voltage across points P1 and P2 will be of a large magnitude when the circuit is idle or when a marking signal is being transmitted from, for example, teletypewriter 'I'I'Y1 .throughtherepeaters to the teletypewriter TTYz.

"Of, coursathe voltage at points P1 and P2 will be equal to the voltage across the loop L1-L2. If the voltages of batteries B1 to B4 are all 130 volts each, for example, then the voltage between points P1 and P2 due to signalin between teletypewriters TTY1 and TTYz will vary from zero The potential at tential at point P1. The voltage between points Pran P2 due to the transmission of signals between'the teletypewriters TTYi and TTYz will be insufficient to overcome the biasing voltage of -:battery-Bu, whichimay be,:for example cf 100 volts; Ience substantially no current will flow through the plate circuit of tube V-and,-there- ,fore, the neutral relay R0 will remain unoperated. -L1-:other words;no signalswill be transmittedto circuit L3 when. signals are transmitted between -teletypewrit-ers'-TTY1 and :TTYI} through the re- :peaters;

It-has i-ust been shown-that the neutralrelay Ru wiil be non-responsive to signals transmitted between the tel-etypewriters 'TTY1 and 'ITYz A di-fferent situation exists when teletypewriter 'ITYo is transmitting signals'over its loop L1-L2 and through the repeaters to the teletypewri-ters TTY1 andTIYz. These signalswill actuate-the relay R0 to repeat these signals to-the circuit L3 where-.tlieymay be recorded-in any -xvelleknown=-manncr, as will now 7 be described.

-When-a "spacing signal is being transmitted rremteletypeWr-iter TTYO through the repeaters to the telety-pewriters .T-TYrand TTYz; the transmitting contacts T0 of; thetcletypcwriterwill be opened in the usual manner-in which case 2. volt- .age-eq-u-al'tothe .additivevalue of the voltages of batteries 31 and .Ba will/appear across the points P1 and-P2. In the case assumed herein- .above for illustrative purposes 1 the potential applied betweenthe pointsP1 andPrwill be approxi-rn-atelyfifio volts, point Pz-being positive with .This large potential will spacing signal will thenbe transmitted to the .circuit Ls.

When a marking signalisbeing transmitted from teletypewriter TTYo to the main station teletypewriters TTY1 and TTY2, the voltage between points P1 and P2 will have a substantial value of, for example, 65 volts in the case assumed thereinabove. The grid of tube V will, however, again be'negative with respect to its cathode because the voltage of battery B11 will exceed the The relay Rc close its markingcontactM. The marking signal will, therefore; be repeated to the circuit L3.

It will thusibe observed that signals coming from the loop circuit 'teletypewriter T'IYo will apply a voltage between points P1 and P2 varying "between a relatively small magnitude and a magnitude which overcomes the biasing voltage of battery B11. This biasing voltage is overcome only for signals arriving from teletypewriter TIYo. Thus the circuit L3 will be selectively responsive to signals emanating from the teletypewriter TTYo, the circuit L3 bein non-responsive to all other signals transmitted between the two repeaters.

The arrangement shown in the drawing and described hereinabove is of special value where it is desired to monitor one of the circuits such as the telegraph loop circuit L1Lz connected to a two-way telegraph repeater circuit carrying signals between two or more main stations. The arrangement permits the monitoring circuit which includes the tube V and circuit L3 to observe all signals coming from the loop circuit teletypewriter T'IYo to the exclusion of all other signals. This monitoring arrangement may be employed for observing conditions in the loop circuit L1L2, as well as the character of the transmission from that loop circuit to the rest of the system.

The impedance Z3 is employed in the circuit described hereinabove for the purpose of reducing the flow of current between the grid and cathode eiectrodes of tube V in response to the large positive potential applied to point P2 with respect to point P1. Without such an impedance the life of the tube might be reduced and its operation might be impaired.

The teletypewriters TTYo, TTYi and T'IYz are given merely for illustration, and it will be understood that they may be replaced by telegraph keys and sounders of well-known type for transmitting ordinary telegraph signals. In other words, the invention may be used not alone for teletypewriter character transmission, but also for telegraph signaling generally.

The values assigned to the various elements which may be employed in this invention are given, of course, for illustrative purposes only, and other values of widely different magnitudes from those assumed and in different ratios may be used in practice Without departing 'rom the spirit of the invention.

While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. The combination of a plurality of two-way telegraph repeaters interconnecting a plurality of stations, a telegraph loop connected to said repeaters so that signals traversing said repeaters from any of said stations may be received by said loop and signals emanating from said loop may traverse said repeaters and be received by stations, a receiving circuit connected across said loop, and means to prevent said receiving circuit from receiving all signals traversing said repeaters except those emanating from said loop.

2. The combination of two main telegraph stations, a telegraph loop circuit, two repeaters interconnecting said. main stations and said loop,

said repeaters including means for relaying signals between the main stations to the loop circuit and from the loop circuit to the main stations, a telegraph circuit bridged across the loop circuit, and means included in said bridging telegraph circuit to prevent the reception of all signals except those coming from the telegraph loop circuit.

In a telegraph system, the combination of two main telegraph stations, a telegraph loop circuit, two repeaters interconnecting said main telegraph stations and said telegraph loop circuit so that signals originating in one of the main stations will be repeated to the other main station and to the telegraph loop circuit, and so'that signals coming from the telegraph loop circuit will be repeated to both main stations, a telegraph receiving circuit bridged across said loop circuit, and means to prevent all signals except those coming from the telegraph loop circuit irom being repeated in said telegraph receiving circuit, said means including a source of voltage and means to overcome the said voltage of said source only when signals are coming from said telegraph loop circuit.

l. In a telegraph system, the combination or" a plurality of main telegraph stations, an auxiliary station, telegraph repeaters interconnecting said main stations and said auxiliary station, said repeaters repeating signals originating in any one of the stations to all of the other stations, a monitoring station bridged across said auxiliary station, and means to relay to said monitoring station all signals originating at said auxiliary station and to prevent the repetition of signals originating in all other stations connected to the system.

5. In a telegraph system employing pulses of direct current for the transmission of signals, the combination of a plurality of telegraph stations, repeaters interconnecting the circuits of all of said stations, 2. telegraph receiving circuit connected to said repeater, said telegraph receiving circuit being bridged across the circuit of but one of said telegraph stations, said telegraph receivpeated to the other stations, 2. telegraph receiv-' ing circuit bridged across said auxiliary station, means including a source of blocking voltage connected in said telegraph receiving circuit to prevent all signals except those originating at said auxiliary station from beingtransmitted to said telegraph receiving circuit, said means in-,

cluding means to overcome. the blocking voltage only in response to signals which originate at sald auxiliary station.

CHARLES ROBERT WALKER, 

